1. Field of the Invention
The present invention relates to a substrate provided with semiconductor films and a manufacturing method thereof. The substrate provided with semiconductor films is a semiconductor substrate having a silicon-on-insulator (SOI) structure.
2. Description of the Related Art
In recent years, the development of VLSI technology has been dramatic, and SOI technology, by which increase in speed and reduction in power consumption can be realized, has been attracting attention. This technology is conventionally a technique in which an active region (channel formation region) of a field effect transistor (FET) made of a bulk single crystal silicon substrate is formed of a single crystal silicon thin film. It is known that when a MOS field effect transistor is manufactured using an SOI structure instead of a conventional bulk single crystal silicon substrate, parasitic capacitance can be reduced, and such a MOS field effect transistor is advantageous in increasing speed.
As an SOI substrate, a SIMOX substrate and a bonded substrate are known. For example, a SIMOX substrate having an SOI structure is manufactured in the following manner: oxygen ions are implanted to a bulk single crystal silicon substrate and heat treatment is performed at 1300° C. or higher to form a buried oxide (BOX) layer; accordingly, a single crystal silicon thin film is formed on a surface of the BOX layer. In the manufacture of a SIMOX substrate, although the depth of the single crystal thin film can be precisely controlled so that the single-crystal thin film can have even thickness, since implantation of oxygen ions can be controlled with precision, there are problems in terms of operation time and cost because implantation of oxygen ions takes a long time. Further, another problem is that the single crystal silicon thin film is easily damaged by oxygen ion implantation.
A bonded substrate having an SOI structure is manufactured in the following manner: two single crystal silicon substrates (a base substrate and a bond substrate) are bonded together with an oxide film interposed therebetween; and one of the single crystal silicon substrates (the bond substrate) is thinned from a rear surface (the surface that is not bonded) so that a single crystal silicon thin film is formed. As a method of thinning the substrate, it is difficult to form an evenly thin single crystal silicon thin film by grinding and polishing; therefore, a technique of utilizing hydrogen ion implantation called “Smart Cut (trademark)” has been suggested (see Patent Document 1: Japanese Published Patent Application H5-211128).